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UNITED STATES DEPARTMENT OF AGRICULTURE 

BULLETIN No. 740 

Contribution from the Bureau of Chemistry 
CARL L. ALSBERG, Chief 


Washington, D. C. V January 13, 1919 




A STUDY OF SOME OF THE CHEMICAL CHANGES WHICH 
OCCUR IN OYSTERS DURING THEIR PREPARATION FOR 
THE MARKET. 

By Edward E. Smith, Junior ChemistJ 


4 


CONTENTS. 


Page. 


Scope of investigation. 1 

Commercial treatment of oysters. 2 

Experimental work. 3 

Methods of analysis. 3 

Series 1. 4 

Series II. 6 


Page. 

Experimental work (continued): 


Series III. 8 

Series IV. 9 

Series V. 13 

Summary. 23 


SCOPE OF INVESTIGATION. 

This bulletin gives the results of an investigation to determine the 
amounts of ammoniacal nitrogen, amino-acid nitrogen, moisture, 
total solids, ash, and sodium chlorid present in oysters under the 
various conditions through which they pass in ordinary commercial 
practice in the oysterhouse, and to ascertain the effect of washing 
and soaking on both the chemical composition and physical condition 
of the oysters. The investigation was conducted during the fall and 
winter of 1914 - 15 , in certain oysterhouses in Connecticut, selected 
as being representative of the oyster industry throughout the North 
Atlantic States. The oysters used were grown in various beds, rang¬ 
ing from New Haven, Conn., on the east, to Raritan Bay, N. J.' on 
the west. As work was done in several houses, each using a different 
method of treatment of the stock, the methods given represent 
commercial practice at that time and in that locality, hut may not 
be representative of later practice or other localities. The experi¬ 
ments which were made to show the results of various special treat¬ 
ments do not represent commercial practice. 

1 The writer wishes to express his indebtedness to Dr. E. D. Clark and Mr. L. H. Almy, who instructed 
him in the methods of determination of ammoniacal nitrogen and amino-acid nitrogen; to Mr. Carleton 
Bates and Dr. Lester Round, who assisted materially in planning the work and under whose direction 
it was carried out; and especially to Mr. R. W. Lamson, without whose help Series V would have been 
impossible. 

77345°—19—Bull. 740 1 


) » 
> / > 







































2 BULLETIN *740, U. S. DEPARTMENT. OF AGRICULTURE. 

COMMERCIAL TREATMENT OF OYSTERS. 

As a slight knowledge of the methods of handling oysters is neces¬ 
sary for a clear understanding of the various subjects touched upon 
in this bulletin, a brief outline of the essential features involved in 
the preparation of oysters for the market, beginning with the dredging 
of the mature oysters, that is, those which are three or four years of 
age, will he given first. 

Oysters are grown in water of a salinity ranging from 1.5 to 3.5 
per cent, calculated as sodium chlorid, the average being about 2.5 
per cent, and are covered to a depth of from 5 to 50 feet at mean low 
tide. In many cases the beds are so far from the oysterhouse that 
upon arrival the oysters may have been out of water for several days. 
For the beds near the house the period is shortened to a few hours. 
“Shucking” oysters, the process of opening the shells and removing 
the meats therefrom, is always done by hand, and those engaged in 
the work are called “shuckers.” The shucker puts the oyster meats 
into a perforated dipper holding 1 gallon. From the shuckers’ dippers 
the oysters are emptied upon the “riffles,” inclined, corrugated metal 
boards, down which a thin stream of water runs. The slight bumping 
caused by the corrugations tends to remove the bits of shell which 
may cling to the body of the oyster, and the water both hastens its 
progress and washes off most of the dirt wdiich it has acquired during 
the process of opening. From the riffles the oysters slide through 
metal chutes to the sorting table, where they are graded and those 
not fit for food are culled out. In Connecticut the following grades 
of oysters are recognized: (1) “Straights,” the name given to the 
entire output of the plant, not graded, with only those unfit for food 
removed; (2) “counts,” very large oysters, not mutilated in opening, 
perfect in shape and color; (3) “selects,” smaller than “counts,” but 
larger than the ordinary run of stock, unmutilated and perfect in 
shape and color; (4) “standards,” the ordinary run-of stock from 
which the “counts,” “selects,” and “culls” have been removed. 

From the sorting table the oysters slide down metal chutes to the 
washing and chilling tanks, where they are thoroughly washed in 
running water, and chilled by means of ice, if the weather is warm 
enough to require it. The method of washing and chilling oysters 
had changed materially in the years immediately preceding the time 
of this investigation, and, instead of only one method, several methods 
were in use. The old method of preparing shucked oysters for the 
market consisted in washing the stock as received from the shucker 
upon a perforated “skimmer board,” by means of running water 
from a hose, the oysters being moved about with a paddle during 
the process. The oysters were then placed in tanks of ice water with 
chunks of ice, and chilled for a period of time not exceeding 20 
or 30 minutes, Mechanical devices, however, had been invented 

0* Ol; j* * 

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<b & 

* 


CHEMICAL CHANGES OCCURRING IN OYSTERS. 


3 


for the washing and chilling of the shucked oysters, and in 1914-15 
the,air-agitation system of washing was in general use in the larger 
plants. In this system, from 20 to 30 gallons of oysters are placed 
in a tank of water, ice is added if necessary, and the whole is agitated 
by means of a blast of air blown in through the perforated bottoms 
of the tanks. A constant flow of fresh water is maintained. In this 
way a very thorough washing is secured. With the change in the 
method of handling, however, the oysterman did not modify the 
length of time for washing and chilling, which resulted in a great 
gain in the bulk of the oysters, due to osmotic action. For in the 
old method of washing, the oysters remained stationary in the 
bottom of the tank, their mass was slowly pervious to water, and 
osmosis could not take place to any extent, whereas in the latter 
method each individual oyster was constantly exposed to the action 
of fresh water for a period of from 20 to 30 minutes. As a result, 
the oysters lost a marked proportion of their soluble constituents, 
and due to the process of osmosis became greatly distended. 

From the washing and chilling tanks, the oysters were run out 
upon “skimmers,” which are perforated metal tables, to drain. 
'They were stirred about upon the skimmers with metal paddles until 
they were thoroughly drained, then were run off into cans, which 
were immediately sealed and stored in a refrigeration room at a 
temperature of about 33° F. Stock was not usually kept in the 
refrigerator more than one or two days; in fact, it was usually 
shipped the morning after packing. 

EXPERIMENTAL WORK. 

METHODS OF ANALYSIS. 

1. Preparation of sample .—The sample of oysters is drained in a 
colander for two minutes, with gentle shaking or stirring to facilitate 
drainage, the liquor being discarded. After draining, one pint of 
the drained meats is ground in a meat chopper, No. 2, using the 
next-to-finest blade, and thoroughly mixed. The required amount 
of sample is weighed out immediately, as evaporation causes serious 
errors in a short time. 

2. Amino-acid nitrogen .—Weigh out 100 grams of the finely- 
ground oyster meat upon the rough balance, wash into a 500 cc 
volumetric flask, make up to the mark with distilled water, and 
shake thoroughly every 10 minutes for 1 hour. Allow to settle, and 
pour off the supernatant liquid. Upon this liquid the determination 
for amino-acid nitrogen is run according to Sorensen’s method. 1 

3. Ammoniacal nitrogen .—This determination was made by Folin’s 
method, 2 aerating for exactly 2 hours, and using 20 grams of the 

i Allen’s Commercial Organic Analysis, 4th ed., 7:262. 2 Am. J. Physiol., 1903, 8;343. 








4 


BULLETIN 740, U. S. DEPARTMENT OF AGRICULTURE. 


finely-ground oyster meats, weighed to within 0.1 gram. Tenth 
normal solutions of acid and alkali were used. 

4. Total solids .—Place a thin layer of dried shredded asbestos on 
the bottom of a thin lead dish, add a short glass rod, and weigh the 
whole. Add about 5 grams of the ground sample, and weigh as 
quickly as possible. Evaporate to dryness on the steam bath, and 
dry for exactly 4 hours in a water-jacketed oven at the temperature 
of boiling water. Weigh, and calculate the percentage of total 
solids. During evaporation, the meat is stirred occasionally with 
the glass rod. This stirring with the asbestos prevents the formation 
of a crust which would hinder evaporation. 

5. Moisture .—Determined by difference from the total solids 
results. 

6. Ash .—Weigh about 5 grams of the finely-ground sample as 
quickly as possible into a previously ignited and weighed platinum 
dish or crucible, drive off moisture at a moderate heat, and ignite at 
the dullest red heat until the ash is gray in color. Extraction with 
water, followed by a second evaporation and ignition, may be neces¬ 
sary to secure a clean gray ash. Weigh, and report as percentage of 
original sample. 

7. Salinity . 1 —Extract the ash obtained in the .preceding deter¬ 
mination with hot water, cool, and titrate against silver nitrate 
solution containing 29.0575 grams of silver nitrate per liter of solu¬ 
tion at room temperature. As indicator, use one or two drops of a 
10 per cent solution of potassium chromate. One cc of this silver 
nitrate solution is equivalent to 10 mg of sodium chlorid. Calculate 
all chlorin as sodium chlorid, and report as percentage present in 
original sample. 

SERIES I. 

In this series, determinations for amino-acid nitrogen and ammo- 
niacal nitrogen only were run. A summary of results is given in 
Table 1. 

The column headed “Shucker” represents oysters as taken from 
the shuckers’ dippers; “Riffle,” oysters taken from the chute below 
the riffle-boards; “Commercial package,” oysters after washing 
and chilling, packed into cans ready to go into the refrigerator; 
“Refrigerator,” oysters from the same day’s run as those upon the 
same line in the preceding columns, but sampled from the cans 
remaining in the refrigerator one or two days later. 

i These results are not exactly accurate, due to the fact that all the chlorin is not in the form of sodium 
chlorid. As no analysis for oyster ash could be found in the literature, and there was no time to make such 
analyses, the plan of calculating all the chlorin as sodium chlorid and reporting it as salinity was adopted. 
Since all the data have been prepared on tins basis, the results are comparable, and the error probably is 
negligible, as the amount present is small in any case, and it is certain that a large proportion of the chlorin 
is present in the form of sodium chlorid. 




CHEMICAL CHANGES OCCURRING IN OYSTERS. 

T able 1 . Percentages of nitrogen obtained at various stages of handling. 


5 


Date. 

Amino-acid nitrogen. 

Ammoniacal nitrogen. 

Shucker. 

Riffle. 

Commer¬ 

cial 

package. 

Refriger¬ 

ator. 

Shucker. 

Riffle. 

Commer¬ 

cial 

package. 

Refriger¬ 

ator. 

1914. 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

Oct. 5. 

0.183 

0.166 

0.128 

0.120 

0.00200 

0.0018 

0.0012 

0.0025 

6. 

.173 

.159 

.1267 

.085 

.00189 

.0015 

.0015 

.0004 

8. 

.171 

.1495 

.115 

.146 

.00042 

.0004 

.0000 

.0010 

10. 

.148 

' .149 

.106 

.116 

.00074 

.0011 

.0000 

.0022 

12. 

.155 

.152 

.106 

.089 

.00154 

.0011 

.0004 

.0000 

13. 

.1658 

.1534 

.1183 

.1237 

.0007 

.0006 

.0007 

.00077 

14. 

. 1439 

. 1433 

. 1142 


0007 

.0007 

.00042 


15. 

.1551 

.1512 

. 1232 

.1378 

.00077 

.0003 

.00024 

.00087 

16. 

.1580 

. 1542 

. 1198 


.00038 

0005 

0000 


Nov. 9. 

. 1522 

. 1582 

. 1249 

1272 

0000 

0000 

0000 


10. 

.1484 

.1400 

.1215 

2.0946 

.00032 

.0002 

.00115 

2.00024 





. 1210 




.00017 

11. 

.1703 

.1670 

.1064 

.1232 

.00021 

.00007 

.0000 

.00073 

12. 

.1813 

. 1692 

. 1305 


.00098 

.00021 

.00073 





. 1311 


.00073 


16. 




. 1540 




.00035 





. 1540 




.00035 

17. 

.1932 

.1727 

.1318 

2 .1084 

.00084 

.0002 

.00098 

2.00031 




. 1429 




.00056 


18. 

. 1635 

. 1585 

. 1204 


. 00049 

.00011 

.0000 


21. 

. 1652 

. 1630 

. 1142 


.00014 

. 0000 

.00024 



1.1658 

». 1429 



i. 00053 

L00025 





2 .1170 




2 .00025 



„Dec. 10. 

.1739 

.1558 

.1188 

.1177 

.00014 

.0000 

.00032 

.0000 

11. 

.1456 

.1479 

. 1367 

.1177 

.00035 

.00007 

.00007 

.00011 

12. 

.1702 

.1685 

.1317 

.1250 

.00014 

.0000 

.00008 

.00011 


1 Selects. 


2 Counts. 


From this table it is apparent that a considerable amount of 
amino-acid nitrogen is present in the oyster as it comes from the shell. 
It is probable that a certain percentage of amino-acid, nitrogen exists 
in the tissues of the oyster body, being either absorbed or formed in 
the process of metabolism. Some of this may be due to bacterial 
activity within the oyster itself. 

The comparatively slight washing of the oyster upon the riffle 
board removes approximately 10 per cent of the amino acids present, 
which shows that a certain proportion of them are present in the mucus 
surrounding the oyster. An additional amount of approximately 
25 per-cent is removed in the washing and chilling process proper, 
which may be explained partly by solution in the wash water, partly 
by the fact that most of the remaining mucus as washed from the 
outside of the oyster, and partly by the increase in volume of the 
oyster due to osmosis. 

From the figures in the “Refrigerator’’ column it is seen that the 
relative figures vary widely. In some cases the percentage of amino- 
acid nitrogen apparently increased, in others remained constant, and 
in still others decreased. This variation is due largely to difference 
in stock used, as*it was found impossible, in a large plant, to be sure 
that the oysters stored were from exactly the same stock as those 
analyzed in the preceding columns. However, if the ammo-acid 
content be taken as indicative of decomposition, it is evident that 







































































6 BULLETIN 740, U. S. DEPARTMENT *0F AGRICULTURE. 

no appreciable amount takes placfe while the oysters are stored in 
the refrigerating room of the oysterhouse for a short time. It is 
interesting to note that the figure for the larger oysters, selects and 
counts, is uniformly smaller than that for the standards of the same 
stock. 

From the results obtained in this series, there appears to be no 
relation between the amino-acid nitrogen and the ammoniacal 
nitrogen present. In general, the figures for ammoniacal nitrogen 
change in the same way as do those for aminoacid nitrogen; but the 
former are so inconsistent, even in duplicates run on the same sample, 
that the whole table is practically meaningless in this connection. 
Similar determinations were run in all the following series of experi¬ 
ments, but as they are in all cases as conflicting as those in Tables 1 
and 2, they have been omitted from all subsequent tables. 

SERIES II. 

In order to prove that the amount of amino-acid nitrogen and 
ammonia present would not indicate decomposition in oysters if the 
water over them was changed occasionally, the following series of 
experiments was run. 

A 5-gallon can of oysters was divided into two lots, and the oysters 
in each were covered with water. One lot was stored at room temper¬ 
ature, the other in a small ice box at a temperature of about 45° F., 
and the water over each lot was changed every day. Determina¬ 
tions were run upon each lot every day for one week. A summary 
of results obtained is given in Table 2. 


Table 2. — Amino-acid and ammoniacal nitrogen as index of decomposition. 


1,1 ■ 

Date of analysis. 

Amino-acid nitrogen 
in portion stored at— 

Ammoniacal nitrogen 
in portion stored at— 

Room temp. 

45° F. 

Room temp. 

45° F. 

1914. 

Oct. 5. 

Per cent. 

0.1290 
.1280 
.1244 
.1075 
.1250 
.1250 
.1215 

Per cent. 

0.1290 
. 1280 
.1272 
.1120 
.0687 
.0676 
.0638 

Per cent. 

0.00123, 

.00116 

.00329 

.00165 

.00392 

.00185 

.00473 

Per cent. 
0.00123 
.00116 
.00259 

Oct. 6.,. 

Oct. 8. 

Oct. 9. 

.000105 

.000098 

.000840 

Oct. 10. 



At the end of this time the oysters soaking at room temperature 
were badly decomposed. In spite of this condition, the amino-acid 
nitrogen content decreased, and the figure for ammoniacal nitrogen, 
though larger than in the same oysters at the beginning of the experi¬ 
ment, was smaller than that found in several samples of fresh oysters. 
The oysters stored in the refrigerator kept much better than those 
stored at room temperature, though they also were slightly decom- 






















CHEMICAL CHANGES OCCURRING IN OYSTERS. 7 

posed at the end of the week. In this lot, the values for both amino- 
acid and ammoniacal nitrogen were smaller at the end than they were 
at the beginning of the experiment. 

Of the two determinations intended to show the amount of de¬ 
composition which has occurred in oysters, it appears that deter¬ 
mination of ammoniacal nitrogen by the Folin method is worthless 
in commercial oyster work for the following reasons: 

(a) The free ammonia and ammonium salts are washed out of the 

oysters nearly as fast as they form. 

(b) The very small amount of standard acid neutralized by the am¬ 

monia makes the probable error relatively large. 

(c) 'W ith alizarin red as an indicator, the color change obtained is 

not sharp, under such conditions. 

For the last two reasons, duplicate determinations often varied 
widely, and no great reliance is to be placed upon the accuracy of 
the determinations; hence, very little weight should be attached to 
the meaning of the results obtained. Often higher ammoniacal 
nitrogen figures were obtained from fresh oysters than from others 
which had undergone decomposition. 

It is believed that the amino-acid nitrogen determination is much 
more consistent and reliable. It is more consistent in that a larger 
amount of solution is taken for titration, which lessens the probable 
error, and in that the end point is easier to locate. The principal 
objection to this determination is that the amino-acid nitrogen con¬ 
tent is not a true indication of the amount of decomposition which 
has taken place in the oysters, for the following reasons: 

(a) Amino acids, being soluble, are washed out of the oysters by 

each change of water in the same way as are the ammonia 
and its compounds. 

(b) Amino acids present a very suitable medium for bacteriological 

growth, and are, therefore, being continuously broken’down 
into some of the simpler compounds already mentioned. 
Therefore, the amount of amino acids present is never a 
measure of the total amount of decomposition, and in many 
cases is a measure of only a very small percentage of it. 
However, the results obtained on oysters undergoing wash¬ 
ing treatments are comparable, and are of great value in 
indicating the amount of soluble matter removed. 

In the study of washing oysters, the greatest reliance is to be 
placed upon the determinations for amino-acid nitrogen, total solids, 
and ash. The figures for moisture are very useful in showing the 
amount of water added to the oysters in the washing processes. 
The determinations for salinity were of little assistance, as the salt 
was removed quite completely in a comparatively brief period of 
washing. 


8 


BULLETIN 740, U. S. DEPARTMENT OF AGRICULTURE. 


i 

SERIES III. 


Since the amino acids present in oysters had been regarded as 
decomposition products, it was assumed that their amounts would he 
at a minimum in oysters fresh from the beds, and would increase with 
the length of time the oysters were out of the water. As some of the 
experiments indicated that this was not the case, the following series 
of experiments was carried out. 

By means of a portable apparatus carried aboard an oyster boat, 
amino-acid determinations were run upon liquors and meats of oysters 
as they came from the water at Princess Bay, New York. Two 
bushels of the same stock were transported to the laboratory at 
South Norwalk the same night. Determinations were run upon 
representative samples of this lot every day for six days, the oysters 
being shucked in the laboratory immediately before analysis. On the 
last day, analyses were also run upon a lot of shell oysters from the 
same locality, which had been stored in the laboratory in baskets for 
four weeks. The results of this series are given in Table 3. 


Table 3. —Percentage of amino-acid nitrogen present in meats and liquors of shell 

oysters, and its variation with age. 


Nov. 30 


Dec. l 
2 

3 

4 

5 
5 


Date. 


1914. 


Meats. 

Liquors. 

Remarks. 

Per cent. 

Per cent. 


0.1938 

0.0588 

Perfectly fresh. 

.1970 

.0625 

Oysters immediately after dredging. 

.1976 

. 0598 

.1640 

.0336 


.1626 

.0353 


.1709 

.0280 


.1709 

.0263 


.1737 

.0224 


.1647 

.0258 


.1645 

. 03S0 


.1594 

.0342 


.1651 

.0302 


.1651 

.0300 


.1720 

.0370 

Oysters from same locality stored in laboratory 4 weeks. 

.1728 

.0377 


This series leaves no doubt that the percentage of amino acids in 
perfectly fresh oysters is much greater than has been supposed. 
This value decreases to a minimum in the first day or two that the 
oysters are out of water, and remains practically constant as long as 
the oysters remain in the shell but do not lose shell liquor. Shortly 
after losing the shell liquor from any cause death ensues with 
attendant decomposition. 

As no further work was done on this very interesting point, no 
conclusions can be drawn at this time. This series seems to indicate, 
however, that some reason other than decomposition must be sought 
to explain the presence of amino acids in fresh oysters. 





















CHEMICAL CHANGES OCCURRING IN OYSTERS. 


9 


SERIES IV. 

In this and the following series, determinations for total solids, ash, 
moisture, and salinity were made, in addition to those for ammoniacal 
and amino-acid nitrogen, as those were found to be the most satis¬ 
factory determinations for showing the effects of commercial washing 
processes. These determinations were run upon oysters in all the 
various stages of preparation in several oysterhouses. The results 
are shown in Table 4. 

77345°—19—Bull. 740-2 



10 


BULLETIN* 740, U. S. DEPARTMENT' OF AGRICULTURE. 


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Washing by Hose and Paddle, on Skimmer-Board. 


CHEMICAL CHANGES' OCCURRING IN OYSTERS. 


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12 


BULLETIN 740, U. S. DEPARTMENT OF AGRICULTURE. 


It had been assumed previously that the composition of oysters in 
the shell would be identical with that of oysters taken from the 
shuckers’ dippers. Table 4 shows that this is not the case, that 
there is a slight but well-defined difference in composition. The 
percentage of total solids and other constituents except water is 
greater in the samples from the shuckers than in the sample of the 
same stock shucked in the laboratory immediately before analysis, 
while the percentage of water is correspondingly less. This difference 
probably is due to the fact that the oysters drain for half an hour or 
more while in the shuckers’ dippers, and tend to lose a certain amount 
of their body fluids, shell liquor, and adhering mucus. The shell 
stock, being opened in the laboratory, had had less time in which to 
lose water, and, therefore, was always poorer in solids., This marked 
difference in composition between oysters which it would seem at 
first glance should be of identical composition, shows very plainly 
that the stock for each determination must he handled in exactly the 
same way every day if the results are to be comparable. 

Table 4 is of great interest in showing the composition of oysters 
during the various stages of progress through the oysterhouse, and 
it shows also in a very striking manner the difference between the 
old and the new methods of washing oysters, to the discredit of the 
new methods, if amount of total nutrients is a proper criterion. 
With the purpose of plainly showing this difference, the table has been 
arranged in two parts, the analyses of oysters washed by the modern 
method of air agitation in tanks and the analyses of stock washed by 
the old method upon a perforated skimmer. 

Of the substances determined, amino-acid nitrogen and total solids 
are taken for comparative purposes, as they are the most consistent 
determinations made and most clearly represent the condition of the 
oysters examined. The amino-acid nitrogen represents a truly 
soluble constituent which would be dissolved out of the oysters by 
the wash water. The total solids, though including most or all of the 
amino-acid nitrogen, are in the main insoluble substances whose 
apparent diminution in quantity is due largely to the distention of the 
bodies of the oysters because of osmosis and loss of particles of solid 
meat in handling or washing. A glance at the average values of 
amino-acid nitrogen and total solids for the two classes of washing 
shows that the content of both is much higher in oysters washed by 
the old method than in those washed by the modern one. A brief 
analysis of the results will show exactly how the two sets of figures 
compare. Taking the amount of each of these substances present in 
the shell stock as a basis upon which to calculate the losses, this 
figure may be called 100 per cent. Thus, the amounts of each of the 
constituents are expressed in percentages of the amount present in 
the same stock while in the shell. For the shucked stock and the 
commercial package, then, the figures in Table 5 are obtained. 


CHEMICAL CHANGES OCCURRING IN OYSTERS. 


13 


Table 5. —Average values of amino-acid nitrogen and total solids of oysters washed 

by both methods. 

(Shell stock, 100 per cent.) 


Determination. 

Old 

method. 

New 

method. 

Shucker: 

Amino-acid nitrogen. 

Per cent. 
104.8 

Per cent. 
106.2 

Total solids.7. 

109.4 

107.3 

Commercial package: 

Amino-acid nitrogen. . 

95.0 

72.2 

Total solids. 

94.0 

76.0 



Considering the comparatively small number of determinations 
made, and the multiplication of error involved in expressing the 
various fractions as percentages, the figures in Table 5 are very 
satisfactory checks. They show that in the old method of washing 
the finished product contains, in a given volume, about 94 per cent 
of the food value possessed by the same oysters in the shell, whereas 
in the modern method of washing this figure falls to a percentage of 
about 74 per cent. 

This series, however, does not indicate in any way the cause of the 
loss, as the amino acids disappear at the same rate as do the total 
solids. This loss may he due almost entirely to osmosis, or it may 
be due in part to solution in the wash water of soluble parts of the 
oyster, or to both. That there is a loss of soluble matter in the wash 
water there is no doubt. This is proved by the complete disappear¬ 
ance of sodium chlorid after a comparatively short period of washing. 
Sodium chlorid and other crystalloids would wash out much faster 
than the soluble protein compounds, which are colloids, hut if the 
sodium chlorid disappears it is certain that other soluble constituents 
tend to disappear also. 

SERIES V. 

In order to determine, if possible, just what proportion of the 
apparent loss of the various constituents is due to osmotic distention 
and what proportion is due to solution in the wash water, and also 
the general chemical effect of all kinds of oyster washing, a series of 
experiments was run in which measured volumes of oysters were 
subjected to various washing processes and were both measured and 
* analyzed at various stages of washing. The results of this seiies aie 
given in Table 6, and a mathematical analysis of the results obtained 

is given in Table 7. 

Experiment 1 .—Five gallons of standards were taken from the 
chute immediately before they entered the agitation tank, carefully 
measured, put into an equal volume of water, stirred thoroughly, 
and allowed to stand. Measurements were made of both water and 
oysters every 6 hours for the first day, and every 12 hours thereafter 
for 3 days. The water was renewed after each measurement. Chem¬ 
ical determinations were made once a day upon samples taken in the 













14 BULLETIN 740, U. S. DEPARTMENT OF AGRICULTURE. 

morning. In all these tables allowance has been made for all samples 
removed. Due to the fact that the oystors settled to the bottom of 
the tank and formed a compact mass which was almost impervious 
to water, very little opportunity was offered for osmotic action to 
take place, and the volume of the oysters remained practically con¬ 
stant throughout the experiment. In the periods of disturbance, 
however, which occurred while the oysters were being measured and 
the water was being removed fresh water came into contact with the 
oysters, and some of it remained with them in the bottom. Thus, 
a little osmotic action other than that at the top of the mass took 
place, and solution progressed continuously, though somewhat slowly. 
Since the volume remained practically constant throughout this exper¬ 
iment, it is evident that all the loss observed in this case must be due 
to solution or mechanical loss. In this case mechanical loss was 
small. In commercial pratice oysters never are subjected to such 
long continued action of water, but this experiment proves that a 
large percentage of the substance of the oyster is soluble in fresh 
water, and that osmotic distention is negligible in oysters washed 
in a tank without agitation. As is to be expected, the purely soluble 
constituents show a much more marked decrease than do the total 
solids, which include both soluble and insoluble substances. 

Experiment 2 .—This experiment was carried out in the same way 
as was Experiment 1, with the same purpose in view. On the third 
day, however, the samples were taken from the bottom of the tank 
instead of from a representative sample of the whole, as was usually 
done, in order to determine whether or not the bottom oysters were 
being affected by the water. The results show very clearly that 
they were not being so affected, as the percentages of total solids, etc., 
did not change during 24 hours of soaking. The percentages show 
the same relative decrease as in Experiment 1. 

Experiment 3 .—Having established the fact that a marked pro¬ 
portion of the solid substance of the oyster is soluble in fresh water, 
it becomes desirable to discover what proportion of the apparent 
loss of the various substances is due to actual loss in the wash water, 
and what is due to the increase in volume of the oyster. In this 
experiment, 20 gallons of oysters were taken from the chute imme¬ 
diately before entering the agitation tank, carefully measured into 
one of the tanks, and washed in the regular way, except that the 
washing was continued for one hour. Samples were taken before 
the process was started and at 15-minute intervals during washing. 
Detailed discussion of this and following experiments will be taken 
up later in connection with Table 7. 

Experiment J +.—This experiment was conducted in an oysterhouse 
in which the old system of washing was used. Five gallons of 
shucked oysters were measured out and placed upon the skimmer. 


CHEMICAL CHANGES OCCURRING IN OYSTERS. 


15 


They were then washed for about 5 minutes by means of water from 
a 11-inch hose, the oysters being constantly stirred about with a 
wooden paddle. They were then drained and packed for shipment. 
This represents regular commercial practice in this particular oyster- 
house. 

Experiment 5. —This experiment was conducted in a plant which 
uses the old method' of washing, but in which the oysters are sub¬ 
jected to the action of water in a tank, with occasional agitation by 
means of a paddle, for 20 or 30 minutes, then drained upon a skim¬ 
mer. Seven gallons of oysters were placed in the tank and treated 
as already described. 

Experiment 7. —This experiment was run in a tank, but, instead of 
air agitation, the oysters were stirred constantly by means of a large 
metal paddle. They were drained, measured, and replaced in the 
tank at such intervals that the period of washing between measure¬ 
ments was 10 minutes. Samples were taken before washing was 
begun, and each time the oysters were measured. Washing was con¬ 
tinued until the oysters began to lose markedly in volume, which 
was observed after 50 minutes of washing. 

Experiment 8. —This experiment was conducted in the same man¬ 
ner as Experiment 7, except that it was done in a different oyster- 
house and that the regular air-agitation method was used. 

Experiment 9.—The object of this experiment was to determine 
whether or not oysters lose appreciably in volume on account of 
repeated handling and measurement as done in the preceding experi¬ 
ments. Six gallons of drained oysters were placed in one tank and 
washed for 30 minutes by the regular method, with air agitation. 
Seven gallons of the same stock were washed in the adjoining tank 
with air agitation, but were drained and measured at 10-minute 
intervals, as in the foregoing experiment. 

Experiment 10 .—Having shown that handling oysters during wash¬ 
ing has a marked effect in decreasing the osmotic distention and 
increasing the actual loss of substance, it was decided to run an 
experiment to compare the volumes and chemical composition of 
oysters washed and handled under conditions identical except for the 
time of washing. This experiment was also designed to find out 
what the maximum of osmotic distention would be. Five gallons 
of drained oysters were placed in each of three adjoining tanks and 
washed with the regular water current and air agitation, Tank A 
for 30 minutes, Tank B for 60 minutes, and Tank C for 90 minutes. 
A representative sample of the whole lot was taken before the wash¬ 
ing was begun, and from each tank at the expiration of its period of 

washing. _ , , . 

Experiment 11. —This experiment was made under regular ship¬ 
ping conditions, and was simply a measurement and analysis of 


16 BULLETIN 740, U. S. DEPARTMENT OF AGRICULTURE. 

oysters before and after washing with the regular water current and 
air agitation for 30 minutes. 

Experiment 12 .—This experiment is of the same nature as the 
preceding one, simply measurement and analysis of a commercial 
shipment before and after washing with regular water current and 
air agitation. 

Experiment 13 .—This experiment was carried out in the same 
manner as was Experiment 12, except that enough dairy salt was 
added to the wash water to make the salinity of the solution 2.53 
per cent. The water over the beds where the oysters were grown 
varied from 2.48 to 2.70 per cent salinity, so no osmosis should take 
place. The object of this experiment was to test the correctness of 
the belief commonly held that all the salt must be washed out of 
oysters to have them “keep.” It has been observed since the 
beginning of the industry that oysters tended to spoil if the salt was 
not washed out to below the point where it could be tasted in the 
water; hence the spoiling was connected with the salinity. This 
phenomenon appears to be merely a coincidence, due to the fact 
that the putrefactive bacteria are washed out at about the same rate 
as is the salt. 

Experiment H .—The oysters in this experiment were washed upon 
a skimmer with a hose for 10 minutes, and were stirred constantly 
with a paddle. 

Experiment 15 .—In this experiment the oysters were washed in a 
regular agitation tank by the regular method, except that instead of 
being constantly agitated by a current of air they were stirred every 
5 minutes with a large metal paddle. Thus, the oysters were affected 
by a constant stream of cold water from the bottom of the tank, and 
were thoroughly agitated six times during the experiment. 


Table 6.— Washing experiments (Series 5). 


CHEMICAL CHANGES OCCURRING IN OYSTERS. 


Salinity. 

Per cent. 

0.02 

1 • 

• • 

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■ ■ a 
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0.02 

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Traces. 

0.14 

.03 

None. 

None. 

None. 

0.47 

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Table 6.— Washing experiments (Series 5) —Continued. 


18 


BULLETIN 740, U. S. DEPARTMENT OF AGRICULTURE. 



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20 


BULLETIN 740, U. S. DEPARTMENT OF AGRICULTURE. 


From Table 6 it is apparent that oysters lose a marked proportion 
of their total solids, and therefore their nutritive value, during the 
process of washing. In speaking of these losses the following terms 
are used: 

(а) “ Apparent loss” denotes the entire loss shown by the analysis. 

This loss is due to both osmotic distention and solution or 
suspension in the wash water. 

(б) “Osmotic loss” denotes the loss due to osmotic distention of the 

tissues of the oysters. This is not an actual loss of sub¬ 
stance, but a replacement by an equal amount of water. 

(c) “Actual loss” denotes the loss caused by solution or suspension of 
part of the oyster substance in the wash water. This loss 
is actual, as the substance thus dissolved or suspended goes 
to waste. 

These losses have been calculated for the more important experi¬ 
ments, using as a basis the amount of each substance present in the 
shucked stock. The figures are tabulated in Table 7. 


Table 7. —Losses expressed in percentages of original amounts present. 


Experi¬ 
ment No. 

Figure 

of 

osmosis. 1 

Amino-acid nitrogen. 

Total solids. 

Ash. 

Appar¬ 

ent. 2 

Os¬ 

motic. 3 

Actual. 4 

Appar¬ 

ent. 2 

Os¬ 

motic. 3 

Actual. 4 

Appar¬ 

ent. 2 

Os¬ 

motic. 3 

Actual. 4 


Per cent. 

Percent. 

Per cent. 

Per cent. 

Per cent. 

Percent. 

Percent. 

Per cent. 

Percent. 

Percent. 

3. 

78.3 

27.0 

21.7 

5.3 

40.9 

21.7 

19.2 

47. 7 

21.7 

26.0 

4. 

100.0 

None. 

None. 

None. 

5.6 

None. 

5.6 

27.6 

None. 

27.6 

5. 

80.0 

24.6 

20.0 

4. 6 







7. 

81.8 

36.0 

18.2 

17.8 

30.4 

18.2 

12.2 

41.4 

18.2 

23.2 

8. 

81.4 

40.8 

18.6 

22.2 

33.0 

18.6 

14.4 

63.8 

18.6 

45.2 

9-A. 

81.5 

30.5 

18.5 

12.0 

23.4 

18.5 

4.9 

51.8 

18.5 

33.3 

9-B. 

85.0 

59.4 

15.0 

44.4 

34.7 

15.0 

19.7 

69.2 

15.0 

54.2 

10-A. 

79.0 

35.3 

21.0 

14.3 

23.5 

21.0 

2.5 

52.3 

21.0 

31.3 

10-B. 

70.6 

47.3 

29.4 

17.9 

30.5 

29.4 

1.1 

63.8 

29.4 

35.4 

10-C. 

67.8 

48.7 

32.2 

16.5 

33.6 

32.2 

1.4 

64.2 

32.2 

32.0 

11. 

82.2 

30.8 

17.8 

13.0 

29. 5 

17.8 

11.7 

% 



12. 

73.7 

37.0 

26.3 

10.7 

30.6 

26.3 

4.3 

56.4 

26.3 

30.1 

13. 

100.0 

7.8 

None. 

7.8 

4.7 

None. 

4.7 

8.5 

None. 

8.5 

14. 

92.0 

25.2 

8.0 

17.2 

20.0 

8.0 

12.0 

53.0 

8.0 

45.0 

15. 

82.7 

28.1 

17.3 

10.8 

23.8 

17.3 

6. 5 

51.5 

17.3 

34.2 

Averages.. 



17. 60 

14.30 


17. 46 

8. 59 


17. 46 

32. 77 













1 Percentage of original amount of each substance which would be present if the apparent loss were due 
to osmosis alone. 

2 The entire loss shown by analysis. This loss is due to both osmotic distension and solution or suspen¬ 
sion in the wash water. 

3 The loss due to osmotic distension of the tissues of the oysters. This is not an actual loss of substance, 
but a replacement by an equal amount of water. 

4 The loss caused by solution or suspension of part of the oyster substance in the wash water. This loss 
is actual, as the substance thus dissolved or suspended is washed off and goes to waste. 

Experiment 3 .—Taking the amount of each substance present in 
the shucked stock as 100 per cent for a basis of calculation, it is 
seen that if the decrease in percentage of the various substances 
were due to osmotic distention alone each of these substances would 
have a value of 78.3 per cent at the end of the process, since the 
volume of the oysters increased from 90.86 liters to 116.06 liters. 
The acjtual figures obtained, however, are as follows: Total solids, 73 
















































CHEMICAL CHANGES OCCURRING IN OYSTERS. 21 

per cent; amino nitrogen, 59.1 per cent; ash, 52.3 per cent. Thus in 
this experiment the actual loss of total solids is only 5.3 per cent of 
the original amount present, probably soluble ammo compounds and 
inorganic salts, while the actual loss of amino acids is 19.2 per cent 
and that of ash-forming substances is even greater, amounting to 26 
per cent. As the osmotic loss is in each case 21.7 per cent, it is 
clear that the actual loss of total solids is relatively slight compared 
to it, while the actual loss of amino acids and other soluble constitu¬ 
ents is as great as, or greater than, the osmotic loss. These figures 
do not represent commercial practice, however, for, in general, oysters 
are washed for about 30 minutes. 

Experiment J +.—In this experiment the increase in volume and, 
therefore, the osmotic loss are zero. The actual loss of amino acids 
is also zero, and that of total solids is only 5.6 per cent. The actual 
loss of ash is rather high but is far lower than when the washing is 
done by the other method. 

Experiment 5 .—The results of this experiment show a gain in 
volume of 25 per cent. This makes the percentage figure for each 
substance 80 per cent and the osmotic loss 20 per cent. As the 
derivation of these figures already has been given in detail (Table 
7), it will not be enumerated for this and the following experiments. 

Experiment 7 .—The maximum osmosis was observed at the end of 
30 minutes of washing in this method. The maximum osmotic 
increase was 22.1 per cent, about 5 per cent less than that observed 
in the case of air agitation. As will be shown later, this lower 
value is due solely to the excessive handling inherent in this method 
of repeated measurement and not to any difference in the methods 
of agitation. The percentage of losses will be seen to correspond 
rather closely to those observed in the air-agitation experiments. 
It is interesting to note, however, that at the end of 40 minutes the 
loss of total solids stopped, probably because of shrinkage in volume 
caused by the excessive handling already mentioned. The per¬ 
centage of amino acids, however, continued to fall. The ash was 
apparently reduced to a minimum, the remainder being practically 
all insoluble. The percentages in Table 7 are calculated from the 
results at the end of 30 minutes, so that they closely represent com¬ 
mercial practice. 

Experiment 8 .—In the calculated results of this experiment the 
30-minute results are used, as these are representative of commercial 
practice. It will be observed that these results agree very closely 
with those obtained in Experiment 7, except in the case of ash. This 
difference is probably explained by the fact that the stock -came from 
widely scattered beds, and the inorganic constituents were probably 
dissimilar. 



22 BULLETIN 740, U. S. DEPARTMENT OF AGRICULTURE. 

Experiment 9 .—These results show clearly that handling has a 
great effect in reducing the amount of increase. The contents of 
Tank A increased 22.8 per cent in volume in 30 minutes of continuous 
washing, while the contents of Tank B increased only 17.71 per cent 
in 60 minutes of equally vigorous but intermittent washing. The 
difference is caused by the intervals of draining and stirring about 
upon the skimmer, in which the oysters lose water. 

Experiment 10. —From the results of this experiment it is apparent 
that oysters are capable of enormous distention and that the limit 
is not reached even with 90 minutes of washing. This experiment 
also seems to indicate that the great actual losses observed in Experi¬ 
ments 3, 7, 8, and 9-B were due to the excessive handling inherent 
in the method of measurement during washing. It is seen from this 
experiment that, even after 90 minutes’ washing, the actual loss of 
total solids is comparatively slight and is probably accounted for 
almost entirely by the great actual losses of amino acids, ash, and 
salt. The osmotic losses, however, are very great, as 32.3 per cent 
of the total solids originally present have been replaced by water, 
and the apparent loss is 33.6 per cent. As in the hard northern 
oysters very little of this added water is given off in shipment, it is 
clear that the consumer may be paying oyster prices for a great deal 
of added water. In one case a 5-gallon commercial package of 
oysters which had been increased in volume 35.7 per cent was shipped 
to a market four days away, and arrived and was sold in apparently 
the best of condition. The meats were sound and plump, and the 
liquor above the oysters was only the usual thick, dense mucus. 

Experiment 11 .—These results are in accord with other results of 
similar experiments, showing a marked loss of solids. The ash figures 
are omitted, as the ash analysis showed a doubtful value which is not 
in accord with the other figures. It was too high, probably caused 
by the presence of a small fragment of shell. 

Experiment 13. —The results of this experiment are very interesting, 
in that they show the increase in volume of oysters during washing to 
be due purely to osmosis, and the soluble parts of the oysters to be 
less soluble in salt water than in fresh. 

Experiment H. —This represents commercial practice in some 
oysterhouses, and the results of this experiment are comparable with 
those of Experiment 4, except in that the washing was continued for 
10 instead of 5 minutes. A comparison of the two sets of results shows 
that the losses are much greater in the second case, as is to be expected. 
As has been pointed out, in this type of washing some of the solid 
matter of the oysters is forced through the perforations of the skimmer 
during washing and is thus lost. 

Experiment 15. —By comparison of the results of this experiment 
with those of Experiment 9-A ; which was run on the same kind of 


CHEMICAL CHANGES' OCCURRING IN OYSTERS. 


23 


stock but with air agitation, it is seen that they are in very close agree¬ 
ment throughout. This shows that the air has little or no effect as 
such, its effect being only to keep the oysters in motion, so that 
osmosis will attain a maximum value. The results of Experiments 
9—A, 10-A, 11, 12; and 15 all agree fairly well, though differences in 
stock and in methods of handling cause rather large discrepancies in 
some cases. 

SUMMARY. 

1. The determination of ammoniacal nitrogen by the Folin method 
is of very little value in estimating the amount of decomposition which 
has occurred in oysters during preparation for the market, because of 
the repeated washings to which they are subjected. 

2. For the same reason the determination of amino-acid nitrogen 
also is useless in estimating decomposition in oysters undergoing 
commercial treatment, although it is a reliable index of the amount 
of washing or soaking which the oysters have received. 

3. A marked loss of oyster solids and of ash constituents occurs on 
washing oysters with fresh water. 

4. Oysters covered with water, hut not agitated, are not appreciably 
affected by osmosis, except in relatively long periods of time. Solu¬ 
tion proceeds slowly, but amounts to a large percentage of the solids 
originally present in the course of two or three days. 

5. If oysters are agitated in fresh water, either by mechanical means 
or by means of a blast of air, a large increase in volume results in a 
short space of time, amounting to as much as 35 per cent in 30 min¬ 
utes, and to as much as 50 per cent in 90 minutes in these experiments. 
This increase is believed to be due to osmotic action. As many 
shucked oysters prepared for the market are washed by this method 
and sold by measure, it follows that the consumer may be buying 
added water. 

6. When oysters were washed in unpolluted water of approximately 
the same salinity as that in which they were grown, no increase in 
volume was found to occur, the actual loss of nutrients was slight, 
and the oysters were cleaned as effectually as they were by being 
washed in fresh water. 

7. The old method of washing oysters on a skimmer with a hose 
and paddle gives much less osmotic loss, and, therefore, a much higher 
content of total solids than does the method of washing by a water 
current and air agitation. 

8. The amount of osmotic distention of which oysters are capable 
has not been determined. It is at least 50 per cent of the original 
volume in the oysters under experimentation. 

9. These experiments seem to indicate that there is no connection 
between soaking and “bleeding' ; in the commercial package (that is, 




24 BULLETIN 740, U. S. DEPARTMENT OF AGRICULTURE. 

giving off the water, which forms a layer in the upper part of the 
container). 

10. Interrupted washing (draining and measuring during washing) 

results in a smaller osmotic increase than does continuous washing 
for the same length of time. * , 

11. The relation of osmotic loss to actual loss varies with the solu¬ 
bility of the substance in question. Thus, in the average of all the 
experiments, in the case of total solids made up of insoluble and 
soluble constituents, the ratio of osmotic loss to actual loss is approxi¬ 
mately 2:1; for amino-acid nitrogen, all of which is soluble, but 
which goes into solution slowly, the ratio is approximately 1:1; and 
for ash-forming substance, which is composed largely of soluble 
inorganic compounds, the ratio is approximately 1:2. 


I 


✓ 


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OF THIS PUBLICATION MAY BE PROCURED FROM 
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»sfeW 


Gaylord Bros, 

M akers 

Syracuse, N. Y. 
PAT. JAN. 21 , 1908 






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